Cipher_Mode and AEAD_Mode improvements

See PR #552

- Add Cipher_Mode::reset() which resets just the message specific state and allows encrypting again under the existing key
- In Cipher_Mode::clear() (at some planes) use cipher->clear() instead of resetting the pointer which would make the cipher object unusable
- EAX_Decryption::output_length() bugfix?! Now its possible to decrypt an empty ciphertext (just a tag)
- Bugfix for GCM_Decryption::finish()
- set tag length in GCM_Mode::name()
- Cipher_Mode tests: add tests for reset()and process()
- AEAD_Mode tests: add tests for reset(), clear(), update() and process()

1 files changed, 5 insertions, 0 deletions

diff --git a/src/lib/modes/aead/gcm/gcm.h b/src/lib/modes/aead/gcm/gcm.h
index 6468cbd9c..463e69a3b 100644
--- a/src/lib/modes/aead/gcm/gcm.h
+++ b/src/lib/modes/aead/gcm/gcm.h
@@ -1,6 +1,7 @@
 /*
 * GCM Mode
 * (C) 2013 Jack Lloyd
+* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -37,6 +38,8 @@ class BOTAN_DLL GCM_Mode : public AEAD_Mode
 
       void clear() override;
 
+      void reset() override;
+
       std::string provider() const override;
    protected:
       GCM_Mode(BlockCipher* cipher, size_t tag_size);
@@ -128,6 +131,8 @@ class BOTAN_DLL GHASH : public SymmetricAlgorithm
 
       void clear() override;
 
+      void reset();
+
       std::string name() const override { return "GHASH"; }
    protected:
       void ghash_update(secure_vector<byte>& x,